ACF can be prepared according to well known methods, as for example described in Helvetica Chimica Acta, Vol. 65(Nr. 149), Fasc. 5, 1982, 1531. The synthesis of ACF leads to a racemic mixture of α- and β-ACF which can be separated by selective crystallization and thus precipitation from the reaction mixture. Usually the β-ACF is the desired product, as it is a valuable starting material used in the manufacture of inter alia cytidine derivatives, such as capecitabine. Capecitabine is the active ingredient of the medicament Xeloda™. The ACF synthesis can be summarized according to the following reaction scheme 1:

EP 0 021 231 as well as WO 2005/040184 disclose the further reaction of the unseparated ACF racemic mixture, containing both α- and β-ACF, to a final product. The separation is thus only carried out subsequent to the reaction of the β-anomer to the desired end product.
In any of the known methods the remaining, residual reaction mixture (mother liquor) contains about 8-15 weight-% of not precipitated α/β-Acetylfuranoside (ratio α:β is about 35:65), which is not separated from the reaction mixture. Consequently, and in particular when used on an industrial scale, considerable amounts of valuable β-ACF are wasted, huge amounts of waste residue have to be worked-up and the costs for the entire manufacturing process up to the final product rise significantly.
It is therefore the objective of the present invention to provide an improved method for the recovery of residual, unseparated β-ACF from reaction mixtures remaining from an initial synthesis of ACF, which is in particular usable on a large industrial scale, more particularly in the production of 5′-deoxy-5-fluoro-N-(pentyloxycarbonyl) cytidine (capecitabine). The advantages of the method according to the present invention are the increase of the overall yield of β-ACF, and consequently also of capecitabine per production cycle, thereby reducing the overall production costs. In addition, the present method renders the entire manufacturing more environmentally friendly due to avoiding of unnecessary high amounts of chemical waste. The method according to the present invention can also optionally be repeated in several serially connected cycles, thereby further improving the efficacy of the present method.